Microsoft has issued a work-around to address an Internet Explorer vulnerability that one leading security organisation described as probably "the most dangerous flaw found in Windows workstations" to date.

Meanwhile, Ihug is taking a separate Microsoft flaw so seriously that yesterday evening it posted a notice recommending that customers currently using eMicrosoft Outlook and Outlook Express "consider the use of alternate software ... until such time as Microsoft releases a patch or upgrade for these products". The Ihug message offers links to the mail clients Pegasus Mail and Eudora Light and to the BugTraq report on the security problem.The security sections on the Xtra and Clear Net customer sites still had no mention of the probelm this morning.

Microsoft has now issued a patch for Outlook and Outlook Express to cover the problem. Links to the upgrades and an explanation of the problem are available on the company's Web site. Ihug updated its notice to customers this morning, linking to the Microsoft patch and noting that the patch does not fix the problem for users of Windows 2000.

Victims can be compromised by simply visiting a rogue Web site or by previewing e-mail containing malicious code, without actually opening any attachments or executing files, according to a security flash issued today by the System Administration, Networking and Security (SANS) Institute.

SANS is a nonprofit institute focused on education and research in several information technology areas including information security.

What makes the hole such a dangerous programming error in Windows software is that it allows crackers to potentially take full control of a victim's computer, said Alan Paller, director of SANS.

"It allows [a cracker] to do anything I can do as a user of my computer," Paller said. This includes editing files, deleting them or e-mailing them to remote destinations without a user's knowledge.

"The problem is really serious," said Ryan Russell, manager of information systems at SecurityFocus.com, a California-based security firm and moderator of Bugtraq, a popular security bulletin board.

The hole gives crackers "the ability to access the hard drive of the victim. That is about as serious as it gets. . . . It's usually considered the 'game-over' stage," Russell said.

Even so, there have been no reports of incidents in which companies have been compromised by the vulnerability, Russell said.

And despite its serious nature, "it is silly for SANS to call this the ’most dangerous flaw found in Windows workstations’," said Elias Levy, chief technology officer at SecurityFocus.

"There have been flaws in the past that have been worse," Levy said.

For example, the Multipurpose Internet Mail Extension buffer overflow in e-mail clients such as Outlook, basically allows crackers to plant malicious code that executes even before a user opens an e-mail message, Levy said.

Of more interest is the fact that Microsoft hasn't really implemented a fix but provided only a work-around to the problem, he said.

All users of Windows 95, Windows 98, Windows 2000 and Windows NT 4.0 workstation edition who have installed Microsoft Access 97 or 2000, while running Internet Explorer 4.0 or higher, are vulnerable to this sort of "total compromise," according to the SANS alert.

Microsoft's work-around, posted on its site last week, is to set an Administrator password for Microsoft Access.

This will cause Microsoft Access to prompt the user for a password before any Visual Basic for Applications code is executed within an Access database, according to a Microsoft FAQ on the subject.

Apart from the Internet Explorer Script work-around, Microsoft last week announced a patch for the so-called Office HTML Script vulnerability.

That hole allows attackers to hide malicious files in a victim's computer. But because it can be exploited under only certain limited conditions, it is "considerably less dangerous than the Access problem" according to the SANS report.

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